Effects of reduced energy availability on bone metabolism in women and men

Background: The short-term effects of low energy availability (EA) on bone metabolism in physically active women and men are currently unknown. Purpose: We evaluated the effects of low EA on bone turnover markers (BTMs) in a cohort of women and a cohort of men, and compared effects between sexes. Methods: These studies were performed using a randomised, counterbalanced, crossover design. Eleven eumenorrheic women and eleven men completed two 5-day protocols of controlled (CON; 45 kcal.kg LBM-1.d(-1)) and restricted (RES; 15 kcal.kg LBM-1.d(-1)) EAs. Participants ran daily on a treadmill at 70% of their peak aerobic capacity (VO2 peak) resulting in an exercise energy expenditure of 15 kcal.kg LBW-1.d(-1) and consumed diets providing 60 and 30 kcal.kg LBM(-1.)d(-1). Blood was analysed for BTMs [beta-carboxyl-terminal cross-linked telopeptide of type I collagen (beta-CTX) and amino-terminal propeptide of type 1 procollagen (P1NP)1, markers of calcium metabolism [parathyroid hormone (PTH), albumin-adjusted calcium (ACa), magnesium (Mg) and phosphate (PO4)] and regulatory hormones [sclerostin, insulin-like growth factor 1 (IGF-1), triiodothyronine (T-3), insulin, leptin, glucagon-like-peptide-2 (GLP-2)]. Results: In women, beta-CTX AUC was significantly higher (P = 0.03) and PINP AUC was significantly lower (P = 0.01) in RES compared to CON. In men, neither beta-CTX (P = 0.46) nor P1NP (P = 0.12) AUCs were significantly different between CON and RES. There were no significant differences between sexes for any BTM AUCs (all P values > 0.05). Insulin and leptin AUC5 were significantly lower following RES in women only (for both P = 0.01). There were no differences in any AUC5 of regulatory hormones or markers of calcium metabolism between men and women following RES (all P values > 0.05). Conclusions: When comparing within groups, five days of low EA (15 kcal.kg LBM-1.d(-1)) decreased bone formation and increased bone resorption in women, but not in men, and no sex specific differences were detected. (C) 2017 Elsevier Inc. All rights reserved.